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Periodic Packet Management

Periodic packet management (PPM) is responsible for processing a variety of time-sensitive periodic tasks for particular processes so that other processes on the router can more optimally direct their resources.

Understanding Periodic Packet Management on MX Series Routers

Periodic packet management (PPM) for MX Series routers is responsible for processing a variety of time-sensitive periodic tasks for particular processes so that other processes on the router can more optimally direct their resources. PPM is responsible for the periodic transmission of packets on behalf of its various client processes, which include the processes that control the Link Aggregation Control Protocol (LACP) and Bidirectional Forwarding Detection (BFD) protocols, and also for receiving packets on behalf of these client processes. To enable PPM to send and receive packets on their behalf, the clients establish adjacencies with PPM. When packets are not received from the client, the adjacency is marked as down and the client is informed.

PPM operates in two modes:

  • Centralized

    When PPM is operating in centralized mode, it runs on the Routing Engine only.
    Distributed

    When PPM is operating in distributed mode, it runs on the Packet Forwarding Engine. Currently, Bidirectional Forwarding Detection (BFD), Link Aggregation Control Protocol (LACP), Link Fault Management (LFM), Connectivity Fault Management (CFM), and Virtual Router Redundancy Protocol (VRRP) operate in distributed mode, by default.

If distributed PPM is disabled, the PPM process runs on the Routing Engine only. You can disable distributed PPM for all protocols that use PPM. You can also disable distributed PPM for LACP packets only.

Best Practice:

We recommend that, generally, you disable distributed PPM only if Juniper Networks Customer Service advises you to do so. You should disable distributed PPM only if you have a compelling reason to disable it.

Configuring Periodic Packet Management on MX Series Routers

Periodic packet management (PPM) is responsible for processing a variety of time-sensitive periodic tasks so that other processes can more optimally direct their resources.

Enabling Centralized Periodic Packet Management

When you enable centralized periodic packet management, the ppm process runs on the routing engine only. When you enable centralized periodic packet management, you have disabled distributed PPM. You can enable centralized periodic packet management for troubleshooting to identify if the protocol is having issues while running on distributed mode. If you do not face the issue while the protocol is running on centralized mode, you can narrow down the issue and identify if the issue is because of PFE failure.

Best Practice:

We recommend that, generally, you disable distributed PPM only if Juniper Networks Customer Service advises you to do so. You should disable distributed PPM only if you have a compelling reason to disable it.

To enable centralized periodic packet management:

  1. From configuration mode, enable centralized periodic packet management by specifying the no-delegate-processing statement at the [edit] hierarchy level.
  2. Commit the configuration by using the commit statement.
  3. Clear the current active protocol session on the device by using the clear protocol-name session command. For example, to clear the BFD session, use the following command.
  4. Verify the periodic packet management mode by using the show routing-options ppm command.

    In the output, the distributed field is false and so ppm is centralized.

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